COPENHAGEN (Reuters) - Boris Johnson, the leader of the campaign for Britain to leave the European Union, showed "political amnesia" with his "absurd" comparison between the EU and Adolf Hitler's plan to rule the continent, the EU's Donald Tusk said on Tuesday.
The response of the European Council president to the former London mayor was among the bluntest yet from a Brussels establishment that has been anxious not to stir a backlash in Britain while urging Britons to opt to remain in the bloc.
Britain will hold a referendum on EU membership next month. The Brexit campaign took a three-point lead over the "Remain" campaign in a survey published by polling firm TNS on Tuesday. Two of three polls published on Monday put the "In" camp ahead.
Johnson, a potential prime minister if fellow Conservative David Cameron fails to keep Britain in the EU, told a newspaper that unifying authority in Europe could not work: "Napoleon, Hitler, various people tried this out, and it ends tragically.
"The EU is an attempt to do this by different methods."
Tusk told reporters in Copenhagen that Johnson had suffered "amnesia" and a "dangerous blackout" of memory: "When I hear the EU being compared to the plans and projects of Adolf Hitler I cannot remain silent," the former Polish premier said.
Describing it as an "absurd" argument, he added: "Boris Johnson crossed the boundaries of a rational discourse."
Tusk said the EU was "a common tool, not a superstate", a means for states to cooperate rather than a government for Europe: "The EU may be blamed for many things, but it still remains the most effective firewall against the ever dangerous, and often tragic conflicts among the nations of Europe.
"The only alternative ... is political chaos, the return to national egoisms and in consequence the triumph of anti-democratic tendencies, which can lead to history repeating itself."
A British exit from the EU, already shaken by differences over migration and the future of the euro zone, would rip away its second-largest economy, one of its top two military powers and by far its richest financial centre.